1. Field of the Invention
The present invention is applied to an apparatus for steering rear wheels of a four-wheel steering vehicle by shifting a steering shaft of the rear wheels in the axial direction by means of a driving force of a rotary motor, and relates to a drive train used in a steering apparatus for rear wheels of a vehicle for transmitting the driving force of the motor to the steering shaft of the rear wheels.
2. Related Art
When a failure is caused in the electrical systems of existing four-wheel steering vehicles, including failures in the electric motors and sensors, the steering shaft of the rear wheels is reset by a centering spring to a neutral position that is neither in-phase (where the steering direction of rear wheels would be the same as that of the front wheels) nor reverse-phase (where the steering direction of the rear wheels would be opposite to that of the front wheels). In other words, existing four-wheel steering vehicles rely on a fail-safe concept of resetting the rear wheels to the neutral position in case of emergency.
However, with known four-wheel steering vehicles:
i) In order to obtain a sufficient resetting force to the neutral position, it is necessary to increase the load to the centering spring. Accordingly, an output of the motor must be increased, and certain losses are caused. PA1 ii) In a conventional fail-safe method, when the rear wheels are suddenly operated and returned to the neutral position in emergencies, the resetting operation might affect adversely the driving performance of the vehicle, and as a result of this problem, such a conventional method is not always preferable. PA1 a reduction mechanism driven by the rotary motor, and PA1 a converting mechanism, driven by the reduction mechanism, for converting a rotational motion of the motor to a linear motion for steering of the rear wheels, wherein PA1 a trapezoidally-threaded male screw member having a male screw portion with a trapezoid thread formed in an outer circumference thereof, and PA1 a trapezoidally-threaded female screw member having a female screw portion with a trapezoid thread formed in an inner circumference thereof for engagement with said male screw portion.